The effect of having an affected parent or sibling on invasive and in situ skin cancer risk in Sweden.

Studies suggest that skin cancer aggregates within families; however, the risk of skin cancer associated with having an affected sibling or parent by subtype, tumor site, and age at diagnosis has not been established. The 2006 update of the Swedish Family-Cancer Database was used to calculate standardized incidence ratios (SIRs), representing the ratio of cancer risk among individuals with affected parents or siblings to the general population. Risk of invasive squamous cell skin cancer for individuals with an affected sibling or parent was increased between two- and three-fold compared with that in the general population. For in situ skin tumors, increased SIRs of 1.95-4.30 for squamous cell, Bowen's disease, and actinic keratosis were observed for individuals with affected siblings or parents, and SIRs were generally higher for tumors at sun-exposed versus covered sites. Finally, SIRs for in situ and invasive squamous cell skin cancer increased by increasing number of parental tumors (P< or =0.01). In conclusion, having an affected sibling or parent was associated with an increased risk of skin cancer of varied subtypes compared with that in the general population, and for some subtypes, these familial risks were increased for tumors at sun-exposed sites or by an increasing number of parental tumors.